As is known, magnetic field sensors can be used in a variety of applications. In one application, a magnetic field sensor can be used to sense an electrical current. One type of current sensor uses a Hall effect magnetic field sensing element in proximity to a current-carrying conductor. The Hall effect magnetic field sensing element generates an output signal having a magnitude proportional to the magnetic field induced by the current through the conductor. Typical current sensors of this type include a gapped toroid magnetic flux concentrator, with the Hall effect device positioned in a toroid gap. The Hall effect device and toroid are assembled in a housing, which is mountable on a printed circuit board. In use, a separate current-carrying conductor, such as a wire, is passed through the center of the toroid and is soldered to the printed circuit board, such as by soldering exposed ends of the wire to plated through-holes.
Other configurations of current sensors are known. Other configurations of current sensors are described in U.S. Pat. No. 6,781,359, issued Aug. 24, 2004 and U.S. Pat. No. 7,265,531, issued Sep. 4, 2007, both of which are assigned to the assignee of the present invention and both of which are incorporated by reference herein in their entireties.
Various parameters characterize the performance of magnetic field sensors, e.g., current sensors. For example, a sensitivity of a magnetic field sensor is a change in the output signal of the magnetic field sensor in proportion to a magnetic field experienced by the magnetic field sensor. For another example, an offset voltage is an unwanted DC offset voltage of an output signal from the magnetic field sensor, normally biased at the power supply of the magnetic field sensor divided by two, for example, five volts divided by two or 2.5 Volts. For another example, a linearity is the degree to which the output signal of a magnetic field sensor varies in direct linear proportion to the magnetic field (e.g., current) experienced by the magnetic field sensor.
It is known that some types of magnetic field sensors tend to have sensitivities and offsets that vary with temperature. Sensitivity variation tends to be related to a stress and/or strain imparted on a magnetic field sensing element used in the magnetic field sensor, for example, upon a Hall effect element, as temperature changes, for example, due to expansion or contraction of packaging of the magnetic field sensor or of the substrate on which the magnetic field sensing element is disposed. Offset variation tends to be related to temperature variable characteristics of amplifiers used in the magnetic field sensor.
Magnetic field sensors sometimes employ analog compensation techniques that can adjust gain (i.e., sensitivity) and/or offset with respect to temperature, for example, using varistors or the like. Such techniques can result in sensitivities and offsets that are fairly invariant with respect to temperature, but often at the expense of room temperature accuracy of sensitivity or offset. Furthermore, analog compensation techniques are fixed and not suited for production or field changes to the compensation.
Magnetic field sensors with digital circuits tend to be slower than magnetic field sensors with analog circuits. In other words, magnetic field sensors with digital circuits cannot respond well to rapidly changing magnetic fields (e.g., due to rapidly changing currents).
It would be desirable to provide a magnetic field sensor with the speed advantages of analog circuits yet using a different technique for sensitivity and offset correction versus temperature.